1. Technical Field of the Invention
The present invention relates to a tire with radial carcass reinforcement intended to bear heavy loads and inflated to relatively high pressures, and in particular a tire for aircraft.
2. The Related Art
The radial carcass reinforcements of such tires generally have several plies of textile reinforcing elements, which are anchored in each bead to at least one annular reinforcing element and in most cases to a single bead wire. The reinforcing elements of the carcass reinforcements are wound around the bead wire from the inside to the outside, forming upturns with respective ends spaced radially from the axis of rotation of the tire. The severe conditions under which tires for aircraft are used are such that the fatigue strength of the beads is low, particularly at the upturns of the carcass reinforcement.
A significant improvement in performance is obtained by separating the carcass reinforcement plies into two groups. The first group comprises the axially inner carcass reinforcement plies in the zone of the sidewalls and beads, such plies then being wound around an anchoring bead wire in each bead from the inside to the outside of the tire. The second group consists of at least one axially outer ply in the above zone, which ply is generally wound partially around the bead wire from the outside to the inside of the tire. Such arrangements are known and shown, for example, in U.S. Pat. No. 4,244,414 (FIG. 2).
French patent No. 2,671,517 proposes a solution which is complementary to the above and consists in arranging the edge(s) of the axially outer ply (plies) between the upturns of the axially inner plies.
The fatigue strength of the beads of tires for aircraft must, however, be improved, in particular when these beads are subjected to high overloads which may lead to deformations in height of the order of 50% or more. The large number of carcass plies, generally formed from reinforcing elements made of aliphatic polyamide, which number is necessary to bear the tension due to the test pressure which, as known, must be equal to four times the service pressure, obviously results in the multiplication of the number of the free ends of reinforcing elements, the multiplication of the interfaces between plies, greater hysteresis losses and thus higher operating temperatures, all factors which are liable to increase the fatigue of the beads and limit their fatigue strength.
The solution proposed by the present invention to improve the fatigue strength of the beads of an aircraft tire is to reduce the number of carcass plies turned up about the anchoring bead wire in each bead.
According to the invention, an aircraft tire, inflated to a high pressure and comprising a tread connected to two beads by way of two sidewalls, each bead having at least one annular reinforcing element, includes a crown reinforcement and a radial carcass reinforcement comprising a number of axially inner plies greater than or equal to two, which radial carcass reinforcement plies have textile reinforcing elements. The tire is characterized in that, among the axially inner plies, at least half the total number of axially inner plies are turned up in each bead about at least one bead wire, at least one and at most three of the other axially inner plies being not turned up in any of the beads and having ends situated radially below a straight line XXxe2x80x2, parallel to the axis of rotation of the tire and passing through the radially innermost point of the cross-section of the bead wire, and axially inside a straight line YYxe2x80x2, perpendicular to the axis of rotation and passing through the center of gravity O of the cross-section of the bead wire.
A ply is referred to as not turned up about any annular reinforcing element when the same ply extends from one bead to the other and is not turned up at either of its ends. This arrangement distinguishes the present invention from the teaching of the British patent No. 875,771 in which some of the carcass plies are not turned up at one end but are turned up at their other end.
While providing the number of plies necessary and sufficient to withstand the tensions due to the internal inflation pressures imposed on the tire, the above arrangement furthermore permits a substantial reduction of the number of reinforcing layers under the annular reinforcing elements serving to anchor the carcass reinforcement. This leads to a reduction of the inside diameter of the annular reinforcing elements and, hence, a better positioning of the reinforcing elements, with, consequently, a better distribution of the contact pressures between the seats and flanges of the beads of the tire and the rim seats and flanges, and more uniform clamping on the rim, the net effect being an improved fatigue strength of the beads.
It has been found that, to improve the behavior in the water bursting test, it is advantageous for the axially inner plies which are not turned up to be chosen from the axially innermost plies, that is to say, the plies innermost in the tire.
The carcass reinforcement is advantageously completed by axially outer carcass plies, i.e., plies radially superposed on the axially inner plies in the region of the crown reinforcement of the tire, then extending in the sidewalls axially outside the inner carcass plies and in the zone of the beads along the upturns of the inner plies while being adjacent to them. The outer plies, also formed from textile reinforcing elements, are wound partially around the annular reinforcing element and have ends situated below a straight line XXxe2x80x2, parallel to the axis of rotation of the tire and passing through the radially innermost point of the cross-section of the annular reinforcing element, and axially beyond the ends of the axially inner plies which are not turned up. The number of outer plies provided is preferably equal to the number of axially inner plies that are not turned up.